1. Field of the Invention
The invention relates to processes and devices for determining physical properties of fluids and, more particularly, is directed toward processes and devices for determining the rheological properties of fluids.
2. Description of the Prior Art
Various instruments have been proposed for testing certain viscoelastic properties of fluids including adhesion, cohesion, surface tension, viscosity, and yield stress. One example of such instruments involves relatively rotatable elements having bearing surfaces between which a fluid to be tested is placed. Another example of such instruments involves relatively reciprocable elements having separable bearing surfaces between which a fluid to be tested is placed. In each case, the associated elements are biased to provide a mechanically related indicium of the properties of the fluid between them. One of the major difficulties encountered in the measurement of the viscoelastic properties of fluids other than "ideal" or Newtonian fluids is that the properties being measured may be altered during the act of measurement. Rotational viscometers tend to homogenize the specimens by the act of shearing the sample between the two rotating surfaces. Capillary devices similarly destroy some viscoelastic properties by shearing and by surface tension between the inner wall of the capillary and the fluid being measured. Fluids, which contain substantial solids, i.e. the dry residue after evaporation of the liquid, such as milk, cream, ketchup, mustard, blood, etc. are composed of complex macro molecules, cross linked or other polymers, oriented or random ultrastructures, all of which contribute to their viscoelastic and other physical properties. If subjected to testing for a sufficiently long time, these fluids homogenize during testing and lose their initial characteristics. Such difficulties tend to prevent achieving a high degree of accuracy because the precise physical and geometrical condition of the fluid sample is difficult to predetermine.